1. Field of the Invention
The present invention relates to the field of disinfectant systems for swimming pool and spa water, cooling tower water, and other aqueous media. More particularly, the invention relates to systems utilizing chlorine as a disinfectant, and to compositions and methods for stabilizing and increasing the useful life of the chlorine in such systems.
2. Description of the Prior Art
The steady increase in the number of swimming pools in use each year has given rise to the need for a more effective, safe, and convenient chemical sanitation. Chlorine in various forms in the most widely used chemical for this purpose, since it is both economical and also highly effective in bacteria and algae control. However, its efficiency and effectiveness vary, and depend upon the method used to introduce the element into the pool water and the type of chlorine compound used. Gaseous chlorine, hypochlorites, and chlorinated organics are all used for swimming pool sanitation and exhibit different types of chlorine residuals and various degrees of bactericidal activity, algicidal activity, and chemical consumption. In addition, such external variables as pool usage and climatic conditions have significant effects upon the efficiency of the sanitizing action.
Various approaches have been proposed in the prior art for stabilizing the chlorine in disinfecting systems. For example, in U.S. Pat. No. 2,988,471, issued to Robert J. Fuchs et al. on Jun. 13, 1961, there is described a method for stabilizing chlorine in aqueous solutions against decomposition by exposure to ultraviolet light or by contact with iron and copper. The method involves adding to the aqueous solution cyanuric acid, ammelide or a salt thereof. The loss of active chlorine is reported to be substantially reduced when the weight concentration of the cyanuric acid is greater than the weight concentration of the available chlorine. The use of cyanuric acid to substantially reduce the loss of active chlorine in aqueous systems exposed to sunlight, for example in swimming pools, has received wide commercial acceptance. See also, e.g., U.S. Pat. No. 4,187,293, issued to Nelson on Feb. 5, 1980.
Although satisfactory results are achieved with the use of cyanuric acid, serious problems exist. One problem is the relatively short half life of active chlorine when exposed to sunlight. At 50 ppm cyanuric acid, the chlorine half-life is only seven hours. On a normal sunny day the majority of the chlorine sanitizer is depleted rapidly.
A second problem that exists is the build up of cyanuric acid in the aqueous system. It is recommended that atypically high concentration of cyanuric acid be reduced to below 100 ppm by partial drainage of the pool water and refilling with fresh water. In fact, in commercial pool operations some health officials will close a pool if the cyanuric acid exceeds 70 ppm. Kirk-othmer Encyclopedia of Chemical Technology, 3rd Ed. Vol. 24, p. 430.
In contrast to the present invention, halogenated glycolurils have been proposed in the prior art as the source of disinfecting chlorine. For example, in U.S. Pat. No. 3,165,521, issued to Slezak et al. on Jan. 12, 1965, a method for sanitizing aqueous water systems is disclosed in which haloglycolurils are used as the source of free chlorine to function as a swimming pool sanitizer. The amount of compound used is that which provides satisfactory disinfecting levels of residual chlorine, i.e. about 0.4 to 0.8 ppm. The use of haloglycolurils as the sanitizing agent in swimming pools is also disclosed in U.S. Pat. No. 3,165,521, issued to Lezak. The use of polyhaloglycolurils for controlling algae in water is disclosed in U.S. Pat. No. 3,252,901, issued to Zettler. The use of chlorinated glycolurils in the treatment of sewage is disclosed in U.S. Pat. No. 3,445,383, issued to Horvath et al.
The preparation of glycoluril is disclosed in U.S. Pat. No. 2,731,472, issued to Reibnitz. U.S. Pat. No. 3,071,591, issued to Paterson, discloses a method for the preparation of N-halogenated glycolurils containing both bromine and chlorine for use as disinfecting agents.
Various other sanitizing approaches have involved the use of certain substituted glycolurils. The use of substituted glycolurils in combination with trichlorocyanuric acid and sodium stearate in sanitizing sticks is disclosed in U.S. Pat. No. 3,342,674, issued to Kowalski. The use of chlorinated glycolurils in combination with a metallic hypochlorite in treating sewage is disclosed in U.S. Pat. No. 3,629,408, issued to Horvath. U.S. Pat. No. 3,187,004, issued to Slezak, discloses the synthesis of alkyl and aryl substituted glycolurils and their use in sanitizing swimming pools. This patent discloses the use of N-halogenated glycolurils with alkaline metal salts.
While these various approaches to sanitizing swimming pool water and the like have been proposed in the prior art, there has remained a substantial need for improved compositions and methods providing sustained disinfection of aqueous media. Though many in the past have pursued chlorine-based systems, the useful life of chlorine in such systems has remained undesirably short. Viable commercial approaches have not been forthcoming, and theoretical approaches have been abandoned. The present invention satisfies the need for a stable, effective chlorine-based disinfectant system.